ARTICLE Received 7 Dec 2013 | Accepted 11 Feb 2014 | Published 4 Mar 2014 Radial-arrayed rotary electrification for high performance triboelectric generator Guang Zhu 1,2, *, Jun Chen 2, *, Tiejun Zhang 2 , Qingshen Jing 2 & Zhong Lin Wang 1,2 Harvesting mechanical energy is an important route in obtaining cost-effective, clean and sustainable electric energy. Here we report a two-dimensional planar-structured triboelectric generator on the basis of contact electrification. The radial arrays of micro-sized sectors on the contact surfaces enable a high output power of 1.5 W (area power density of 19 mW cm 2 ) at an efficiency of 24%. The triboelectric generator can effectively harness various ambient motions, including light wind, tap water flow and normal body movement. Through a power management circuit, a triboelectric-generator-based power-supplying system can provide a constant direct-current source for sustainably driving and charging commercial electronics, immediately demonstrating the feasibility of the triboelectric generator as a practical power source. Given exceptional power density, extremely low cost and unique applicability resulting from distinctive mechanism and structure, the triboelectric generator can be applied not only to self-powered electronics but also possibly to power generation at a large scale. DOI: 10.1038/ncomms4426 1 Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, China. 2 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA. *These authors contributed equally to this work. Correspondence and requests for materials should be addressed to Z.L.W. (email: [email protected]). NATURE COMMUNICATIONS | 5:3426 | DOI: 10.1038/ncomms4426 | www.nature.com/naturecommunications 1 & 2014 Macmillan Publishers Limited. All rights reserved.
Transcript
ARTICLE
Received 7 Dec 2013 | Accepted 11 Feb 2014 | Published 4 Mar 2014
Radial-arrayed rotary electrification for highperformance triboelectric generatorGuang Zhu1,2,*, Jun Chen2,*, Tiejun Zhang2, Qingshen Jing2 & Zhong Lin Wang1,2
Harvesting mechanical energy is an important route in obtaining cost-effective, clean and
sustainable electric energy. Here we report a two-dimensional planar-structured triboelectric
generator on the basis of contact electrification. The radial arrays of micro-sized sectors on
the contact surfaces enable a high output power of 1.5 W (area power density of
19 mWcm� 2) at an efficiency of 24%. The triboelectric generator can effectively harness
various ambient motions, including light wind, tap water flow and normal body movement.
Through a power management circuit, a triboelectric-generator-based power-supplying
system can provide a constant direct-current source for sustainably driving and charging
commercial electronics, immediately demonstrating the feasibility of the triboelectric
generator as a practical power source. Given exceptional power density, extremely low cost
and unique applicability resulting from distinctive mechanism and structure, the triboelectric
generator can be applied not only to self-powered electronics but also possibly to power
generation at a large scale.
DOI: 10.1038/ncomms4426
1 Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, China. 2 School of Materials Science and Engineering,Georgia Institute of Technology, Atlanta, Georgia 30332, USA. * These authors contributed equally to this work. Correspondence and requests for materialsshould be addressed to Z.L.W. (email: [email protected]).
The quality of life and sustainable development of modernsociety are largely defined by the available amount ofelectric power. Everything that hallmarks the high-tech era,
from advanced illumination through smart appliances to portableand even wearable electronics, depends on electricity, which hasbecome indispensable in people’s daily life. Although electricity-generating technologies have been developed for two hundredyears, people have never ceased to explore new methodsthrough different mechanisms including photoelectric effect1–3,piezoelectric effect4–6, thermoelectric effect7–9, electrochemicalreaction10–12 and electrostatic induction13–15, among others, inorder to address the rapidly rising demand on electric power.Among them, harvesting mechanical energy is attractingincreasing attentions due to the extensive availability of thetarget resource16–25. Recently we have introduced a new concepton the basis of triboelectrification for harvesting energyfrom various ambient mechanical motions26–28. However, abreakthrough is desperately needed to boost the output power sothat it can be used as an effective power source for practicalapplications. Therefore, it is critical to explore advanced designsand approaches. Besides, other practical issues such as highoutput impedance, mechanical fragility, fluctuation in outputpower and alternating current (AC) output also need to beproperly addressed before the triboelectrification-based generatorbecomes a truly practical new energy technology.
In this communication we report a triboelectric generator(TEG) for producing energy from rotary surfaces with unprece-dented performance. Enabled by a design of two radial-arrayedfine electrodes that are complementary on the same plane, theplanar-structured TEG generates periodically changing tribo-electric potential that induces ACs between electrodes. Operatingat a rotation rate of 3,000 r min� 1, a TEG having a diameter of10 cm can produce an open-circuit voltage (Voc) of B850 V and ashort-circuit current (Isc) of B3 mA at a frequency of 3 KHz.Under the matched load of 0.8 MO, an average output power of1.5 W (an area power density of 19 mW cm� 2) can be deliveredto an external load at an efficiency of 24%, representing a giganticleap in terms of output power by orders of magnitude comparedwith previous reports29,30. The TEG is demonstrated as aneffective measure in harvesting a variety of ambient mechanicalmotions, such as light wind, water flow and body movement.More importantly, a complete power-supplying system is builtthrough integrating a power management circuit with the TEG,which can provide a continuous direct-current (DC) source at aconstant voltage for sustainably driving as well as charging variouscommercial electronics and thus immediately demonstrate thefeasibility of the TEG as a practical technology. Given othercompelling features of the TEG including small volume, lightweight, low cost and proven scalability, it is not only suited toharvest mechanical energy for self-powered electronics, but also itcan be potentially applied to large-scale energy generation.
ResultsDevice structure. A TEG has a multilayered structure, whichconsists of mainly two parts, that is, a rotator and a stator, assketched in Fig. 1a. The rotator is a collection of radially-arrayedsectors separated by equal-degree intervals in between. With eachsector unit having a central angle of 3�, the rotator has a total of60 units. For the stator, it is divided into three components. Alayer of fluorinated ethylene propylene (FEP) as an electrificationmaterial, a layer of electrodes and an underlying substrate arelaminated along the vertical direction. The electrode layer iscomposed of two complementary-patterned electrode networksthat are disconnected by fine trenches in between (Fig. 1b,c).Having the same pattern as that of the rotator, each network is
formed by a radial array of sectors that are mutually connected atone end. The electrode layer is fully imbedded and stationary.This rational design not only leads to structural simplicity butalso accounts for excellent robustness, making the TEG practi-cally reliable and durable. As exhibited in Fig. 1d,e, both therotator and the stator have two-dimensional planar structures,respectively, resulting in a small volume of the TEG. Detailedfabrication process is discussed in Methods.
Electricity generation process. The operation of the TEG relieson relative rotation between the rotator and the stator, in which aunique coupling between triboelectrification and electrostaticinduction gives rise to alternating flow of electrons betweenelectrodes. The electricity-generating process is elaboratedthrough a basic unit in Fig. 2. We define the initial state (Fig. 2a)and the final state (Fig. 2c) as the states when the rotator isaligned with electrode A and electrode B, respectively. Theintermediate state (Fig. 2b) represents the transitional process inwhich the rotator spins from the initial position to the finalposition. Since the rotator and the stator are in direct contact,triboelectrification creates charge transfer on contacting surfaces,with negative charges generated on the FEP and positive ones onthe metal29,31, as illustrated in the cross-sectional view defined byan arbitrary intersection in Fig. 2. Due to the law of chargeconservation, the density of positive charges on the rotator istwice as much as that of negative ones on the stator because ofunequal contact surface area of the two objects.
In open-circuit condition, electrons cannot transfer betweenelectrodes. The open-circuit voltage is then defined as theelectric potential difference between the two electrodes, that is,Voc¼UA�UB. The initial state corresponds to the maximumpotential on electrode A and the minimum potential on electrodeB, which results in the maximum Voc. Such a voltage thendiminishes as the rotator starts to spin. Once the rotator passesthe middle position, Voc with the opposite polarity starts to buildup until the rotator reaches the final state. Further rotationbeyond the final state induces the Voc to change in a reversed waybecause of the periodic structure. The continuous variation of theVoc is visualized via COMSOL in Supplementary Movie 1. On thebasis of the assumption that the thickness of the dielectric layer isfar smaller than the width dimension in Fig. 2, an analyticalmodel can be established, in which any overlapped regionbetween the rotator and the electrodes can be treated as a parallel-plate capacitor without consideration of edge effect15,32. Thenthe Voc can be analytically expressed by the following equationsusing Gauss Theorem. The detailed model is presented inSupplementary Fig. 1 and Supplementary Note 1.
Initial state: Voc 0ð Þ¼ 2d�se0er
ð1Þ
Intermediate state: Voc að Þ ¼ d�se0er� a0� a
a� a
a0� a
� �
ða approaches neither 0 nor a0Þð2Þ
Final state: Voc a0ð Þ ¼ �2d�se0er
ð3Þ
where d is the thickness of the FEP layer, s is the triboelectriccharge density on top of the FEP layer, e0 is the dielectric constantof vaccum, er is the relative dielectric constant of FEP,a is the angle at which the rotator rotates away from the initialstate, and a0 is the central angle of a single rotator unit.
The equation (2) can only be used to illustrate the changingtrend of the Voc (see Supplementary Note 1). The theoreticalpeak-to-peak value of the Voc needs to be calculated by
By substituting the known parameters into equation (4)(d¼ 25 mm, s¼B200 mC m� 2, er¼ 2.1)29, the Voc (peak-to-peak) is theoretically estimated to be B1,000 V.
If the two electrodes are connected as shown by the bottomrow in Fig. 2, free charges can redistribute between electrodes dueto electrostatic induction. At the initial state, induced chargesaccumulate on electrode A and electrode B with charge density of�s and s, respectively. As the rotation starts, free electrons keepflowing from electrode A to electrode B until the rotator reachesthe final state where the charge density on both electrodes isreversed in polarity compared with the initial state. As a result,
the amount of charges in this transport process can be expressedby the following equation
Q ¼ a0
180�s�pðr2
2� r21Þ ð5Þ
where r2 and r1 are the outer radius and inner radius of the TEG,respectively. Again, further rotation beyond the final state resultsin a current in the opposite direction (see Supplementary Fig. 2and Supplementary Note 2 for detailed derivations).
Therefore, AC is generated as a result of the periodicallychanging electric field, which has a frequency calculated as
f ¼ 180va0
ð6Þ
where n is the rotation rate (r sec� 1).
Electrode B
Ele
ctro
de B
Electrode A
FEP
GoldCopper
Acrylic
(Rotator)
(Stator)
Electrode A
Figure 1 | Structural design of the triboelectric generator. (a) Schematic illustrations of the triboelectric generator, which has two parts, that is,
a rotator and a stator. The zoomed-in illustrations at the inner end (b) and the outer end (c) reveal that the two electrodes have complementary
patterns, which are separated by fine trenches in between. It is noted that these drawings do not scale. (d) Photograph of a rotator (scale bar, 1 cm).
(e) Photograph of a stator, in which the through-holes along edges are for mounting purpose (scale bar, 2 cm).
+ + + + + + + + + + + + + + + + + + + + + + + +
Initial state
Rotator
Final stateIntermediate state
–�2�
d
+ + + + + + + +
Open-circuit
Short-circuit
+
+ + + + + + + + + + + + + + + +
Current
–� –�
Intersection
FEP
Electrode A Electrode B
Open-circuit
Short-circuit
Open-circuit
Short-circuit
– – – – – – – –
– – – –
– – – –
– – – –
– – – –
– – – – – – – –
– – – – – – – –
– – – – – – – –
– – – – – – – –
– – – –� �
�0�0 �
+
+ + + +
+
++++
+
Figure 2 | Schematics of operating principle of the triboelectric generator. (a) Initial state in which the rotator is in alignment with electrode A.
The three sections from top to bottom illustrate the three-dimensional schematic, charge distribution in open-circuit condition, and charge distribution
in short-circuit condition, respectively. (b) Intermediate state in which the rotator is spinning away from the initial position at an angle of a. (c) Final
state in which the rotator is in alignment with electrode B. The rotator has rotated a0 away from the initial position.
Electric measurement. To control the rotation rate for quanti-tative measurement, a programmable rotary motor was connectedto the rotator that was in coaxial alignment with the stator. At arotating rate of 500 r min� 1, short-circuit current (Isc) has acontinuous AC output at an average amplitude of 0.5 mA(Fig. 3a). The constant frequency of 500 Hz is consistent with theresult calculated from equation (6). For open-circuit voltage(Voc), it oscillates at the same frequency as that of Isc with a peak-to-peak value of 870 V (Fig. 3b), which corresponds well to thetheoretical value obtained from equation (4) though the slightdeviation is likely attributed to the fact that the actual contact areais less than the apparent device area because of surface roughness.In short-circuit condition, the amount of electrons in a singleelectron-transport process reaches 0.32 mC (Fig. 3c), which cor-responds to an effective DC current (Idc¼DQ/Dt) of 0.32 mA. Itis noticed that the duration of a current peak is determined by theratio between the central angle of a sector and the rotation rate(Fig. 3a). Once an external load is applied, the amplitude of theoutput current drops as the load resistance increases, as shown inFig. 3d. The average output power is equivalent to the Jouleheating of the load resistor, which can be calculated as I2
effective�R,where Ieffective is the effective current defined as the rootmean square value of the current amplitude, and R is the loadresistance. At the matched load of 4.9 MO, the average outputpower reaches 0.23 W at a rotation rate of 500 r min� 1 (Fig. 3d).
Tuning output power. Rotation rate is a major factor thatdetermines electric output of the TEG. A linear relationship canbe derived from Fig. 4a between the amplitude of Isc and therotation rate since higher rate linearly shortens the duration of acurrent peak and thus boosts the current amplitude. In com-parison, the amplitude of Voc remains stable regardless of therotation rate (Fig. 4a) because it is only dependent on the positionof the rotator, as indicated in equation (2). It is found that thematched load is also a variable value, exhibiting a reversely pro-portional relationship with the rotation rate, as diagrammed inFig. 4b. Consequently, linearly rising output power can beobtained at higher rotation rate (Fig. 4b). Given the linearbehaviour of the TEG, it delivers an optimum average output
power of B1.5 W at the matched load of B0.8 MO when oper-ating at a rotation rate of 3,000 r min� 1, which corresponds to anaverage output power density of 19 mW cm� 2. For the first time,the output power from triboelectrification-based generators isboosted to a level where it is sufficiently powerful to drive dailyused electronics, immediately resolving the most critical concernfor the concept of power generation via triboelectrification.
Design parameters, especially the size and the unit centralangle, can also largely influence the output power of the TEG.Figure 4c shows an approximately quadratic dependence of the Isc
and independence of the Voc on the radius of the TEG, which areconsistent with the results in equations (4) and (5), respectively.With the matched load decreasing with the radius, the averageoutput power exhibits a roughly quadratic relationship with theradius (Fig. 4d). In other words, the output power linearly scaleswith the area of the TEG since the triboelectrification is a surfacecharging effect that is area-dependent. Compared with the devicesize, the unit central angle reversely affects the output power. Asrevealed in Fig. 4e, the Isc linearly drops as the central angleincreases, while the Voc still remains stable. Again, the measuredresults fit well with the theoretical model. Consequently, the averageoutput power decreases in almost a linear way if devices with largercentral angle are used (Fig. 4f). Therefore, fine feature size of theunit sector plays a key role in achieving high output power.
Efficiency and reliability. The efficiency of the TEG is defined asthe ratio of the input mechanical power from the motor to theelectric power that is delivered to the load. When driving the TEGat a rotation rate of 3,000 r min� 1, the motor exhibits a loadfactor of approximately 20%, corresponding to an actual torque of0.02 N m delivered to the TEG. Then we can derive the powerinput from the motor to be 6.28 W by using the above values.Given the electric output power of 1.5 W at the same rotationrate, the efficiency is calculated to be B24%. The reliability of theTEG, especially the resistance against mechanical wear, isimportant in evaluating its performance. Here, adhesive wear thatoccurs when two nominally flat solid bodies are in sliding contactapplies to the TEG33. Therefore, the adhesion of the depositedmetal on the rotator largely determines the wear resistance.
0 2 4 6 8 100.1
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–250
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rent
am
plitu
de (
mA
)
Sho
rt-c
ircui
t cur
rent
(m
A)
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put c
harg
e (μ
C)
Time (ms)
Ope
n-ci
rcui
t vol
tage
(V
)
Time (ms)
Time (ms) Load resistance (MΩ)
Average pow
er (mW
)
Figure 3 | Results of electric measurements. (a) Short-circuit current (Isc) at a rotation rate of 500 r min� 1. (b) Open-circuit voltage (Voc) at
a rotation rate of 500 r min� 1. (c) Output charge at a rotation rate of 500 r min� 1. (d) Load matching test at a rotation rate of 500 r min� 1.
Maximum average output power is obtained at the matched load of 4.9 MO.
Special treatment was taken in fabricating the TEG, includingadding an adhesion layer and surface plasma treatment beforemetal deposition34,35. As a result, the TEG shows excellentstability and durability. After continuously producing more than10 million cycles of AC, the output current does not even exhibitany measurable decay or degradation (Supplementary Fig. 3),which firmly proves the reliability of the TEG as a feasibleapproach for practical applications.
Power source for electronics. To demonstrate the capability ofthe TEG as a power source, it was directly connected to regularlight bulbs without using a storage or power regulation unit. Therotation rate was set at 1,000 r min� 1. A total of 20 spot lightswere simultaneously lighted up (Fig. 5a, Supplementary Movie 2),providing sufficient illumination even for reading printed text incomplete darkness (Fig. 5b, Supplementary Movie 3). Moreover,other types of light bulbs that could be driven by the TEGincluded a white globe light (Fig. 5c, Supplementary Movie 4)and 10 multicolor decoration candelabra lights (Fig. 5d,Supplementary Movie 5).
It is noticed that the TEG has high voltage but relatively lowcurrent, resulting in large output impedance and thus affecting itsapplicability as a power source. Besides, fluctuation in outputpower and the AC output current are also concerns in practicalapplications. These issues can be fully addressed by integrating
the TEG with a power management circuit to form a completepower-supplying system. Consisting of a transformer, a rectifier, avoltage regulator and capacitors, the power management circuitas diagrammed in Fig. 6a can deliver a DC output at a constantvoltage of 5 V in less than 0.5 s after the TEG starts to operate(Fig. 6b). The transformer shown in Fig. 6a is able totremendously boost the output current at the expense of theoutput voltage (Supplementary Fig. 4), which substantiallyreduces the output impedance of the TEG. The power-supplyingsystem is suited to a variety of purposes. On one hand, it couldprovide a continuous uniform DC power to drive variouscommercial electronics. As demonstrated in Fig. 6c andSupplementary Movie 6, 10 LED bulbs (0.75 mW each) connectedparallel to output terminals of the circuit were continuouslypowered with full brightness. Moreover, once the output voltagereaches 5 V, the power-supplying system could sustain wirelesstransmissions for five times (Fig. 6d, Supplementary Fig. 5,Supplementary Movie 7) as well as continuous operation of amultifunction digital clock for 60 s (Fig. 6e, Supplementary Fig. 6,Supplementary Movie 8). On the other hand, the system is alsoable to serve as a charging source for batteries. Since 5 V is thestandard charging voltage for most of the commercial portableelectronics, a cellphone automatically turned on once the voltageoutput shot to 5 V due to the operation of the TEG, as visualizedin Fig. 6f, Supplementary Fig. 7 and Supplementary Movie 9.
100 200 300 400 5000
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am
plitu
de (
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25.00 31.25 37.50 43.75 50.000
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plitu
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plitu
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)V
oltage (peak-to-peak) (V)
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)M
atch
ed lo
ad (
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)M
atch
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ad (
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)M
atch
ed lo
ad (
MΩ
)
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er (mW
)A
verage power (m
W)
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er (mW
)
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Figure 4 | Factors that influence the electric output of the triboelectric generator. (a) Amplitude of Isc and peak-to-peak value of Voc with
increasing rotation rate. (b) Matched load resistance and average output power with increasing rotation rate. (c) Amplitude of Isc and peak-to-peak
value of Voc with increasing outer radius of the triboelectric generator (500 r min� 1). (d) Matched load resistance and average output power
with increasing outer radius of the triboelectric generator (500 r min� 1). (e) Amplitude of Isc and peak-to-peak value of Voc with increasing
central angle of a unit sector (500 r min� 1). (f) Matched load resistance and average output power with increasing central angle of a unit sector
Operation in ambient environment. In addition to being drivenby an electric motor for quantitative measurement, the TEG wasfurther tested in normal environment where a series of ambientmechanical energy was harvested. First, energy harvesting fromlight air flow (wind) was demonstrated (Fig. 7a). Artificial breezewas generated at a speed of 6 m s� 1 by an air mover. The wind
perpendicularly blew on a miniaturized three-vane wind turbine(inset in Fig. 7a). Driven by the turbine through a transmissionshaft, the rotator of the TEG spun smoothly, directly providinga power source for lighting up an array of spot lights(Supplementary Movie 10). Such a wind speed falls into class 4defined by Beaufort scale and is much lower than the wind speed
TEG
(r min–1)
Figure 5 | Demonstrations of the triboelectric generator as a practical power source. (a) Photograph of 20 spot lights that are directly powered
by the triboelectric generator in complete darkness (rotation rate: 1,000 r min� 1; scale bar, 5 cm). Inset: demonstration setup (scale bar, 5 cm).
(b) Photograph of printed text on a paper illuminated by the 20 spot lights in complete darkness with the triboelectric generator as a direct power
source (rotation rate: 1,000 r min� 1; scale bar, 3 cm). The font size is 12 points. (c) Photograph of a G16 globe light that is directly powered by the
triboelectric generator in complete darkness (rotation rate: 1,000 r min� 1; scale bar, 3 cm). (d) Photograph of 10 multicolor decoration candelabra
lights that are directly powered by the triboelectric generator in complete darkness (rotation rate: 1,000 r min� 1; scale bar, 3 cm).
0.0 0.5 1.0 1.5 2.0
0
1
2
3
4
5
6
Out
put v
olta
ge (
V)
Time (s)
TEG starts
TE
G
(r min–1)40:1 1,
000
μF
0.01
μF
1,00
0 μF
0.01
μF
5 V
0.00
1 μF
Figure 6 | Demonstrations of the integrated power-supplying system for driving and charging electronics. (a) Circuit diagram of the complete
power-supplying system that consists of a triboelectric generator and a power management circuit. (b) Output voltage of the system reaches a
constant value of 5 V in less than 0.5 s as the triboelectric generator starts to rotate at 3,000 r min� 1. (c) Photograph of 10 LEDs (0.75 mW each)
in parallel that are powered to full brightness by the power-supplying system with ambient background lighting (rotation rate: 3,000 r min� 1; scale bar,
3 cm). The dashed blue box indicates the power management circuit. Inset: photograph of the lighted LEDs in complete darkness. (d) Photograph
of an alarm triggered by a wireless emitter that relies on the power-supplying system (scale bar, 3 cm). Inset: photograph of the ‘panic’ button that
sets off the alarm. (e) Photograph of a multifunction digital clock driven by the power-supplying system (scale bar, 3 cm). (f) Photograph of a cellphone
that is being charged by the power-supplying system (scale bar, 3 cm). As soon as the output voltage of the system reaches 5 V, the cellphone turns
for normal operation of a large wind farm (B10 m s� 1), indi-cating the effectiveness of the TEG in addressing mild agitationfrom air flow. Second, water flow was successfully demonstratedas a target mechanical source (Fig. 7b). The TEG was connectedto the central shaft of a miniaturized water turbine (bottom insetin Fig. 7b). Normal tap water at a flow rate of 5.5 l min� 1 wasdirected into the turbine inlet through a plastic pipe (top inset inFig. 7b), which served as a sufficient driving force for the TEG.Consequently, output power for the spot lights was continuouslyproduced (Supplementary Movie 11). Last but not the least, theTEG could also effectively operate if the input mechanical energyoriginated from gentle body movement. As illustrated in Fig. 7c,the compact-sized TEG in a hand had pieces of inertia mass fixedon the rotator. As the hand swung back and forth in smallamplitude, asymmetric inertia resulting from the extra massinduced relative rotation between the hand-held stator and thefree-standing rotator. The spot lights again served as an explicitindicator of the produced output power from the TEG(Supplementary Movie 12).
Furthermore, with input mechanical energy fed from the aboveambient motions, the power management circuit was stillfunctional and showed a linearly increasing output voltage as itwas being charged up by the TEG (Fig. 7d). Therefore, thesedemonstrations firmly prove that the TEG can fully operate innormal environment by utilizing ambient mechanical energyfrom a variety of sources, indicating its widespread applications inharvesting human motions and even natural energy.
DiscussionCompared with other existing technologies for power generation,the TEG is distinct in basic mechanism from fundamental pointof view. The usual electric generator mostly relies on electro-magnetic induction, an effect from the coupling between bulk
magnetic materials and conductors. In comparison, our generatordepends on triboelectrification, a universally applicable chargingeffect that is confined only at contact surfaces. Such a distinctionin fundamental mechanism differentiates our generator from thetraditional generator in a number of major aspects. In general, theTEG is a complementary approach in parallel to the traditionalelectric generator. Its uniqueness as well as real advantages iselaborated below.
From the structure point of view, the usual generator has abulky structure since the output power heavily depends on suchfactors as the number of coil turns, the diameter of metal coils,the coil geometry and the size as well as weight of magnets.The shrinkage in size results in substantial deterioration inoutput power due to insufficient electromagnetic couplingand other parasitic effects36. Therefore, the usual generatornormally has relatively large size and weight for producing adecent output power. For example, our test on a commercialmini-sized generator of 8.2 cm3 in volume and 29 g in weightshowed an optimum output power of 0.13 W when rotating at1,800 r min� 1. In comparison, our generator relies on tribo-electrification, a surface charging effect. The simple stator–rotatorstructure has a two-dimensional planar configuration. In additionto using hard sheets as substrates (Fig. 1), we can further extendthe substrate materials to plastic thin-film materials that areflexible such as polyimide by using photolithography and laserpatterning techniques (Supplementary Fig. 8, Methods). Havingthe same radius and radial periodicity as the device in Fig. 1, thethin-film TEG gave the same level of output shown in Fig. 2. It isonly 75mm in total thickness, 0.6 cm3 in volume, and 1.1 g inweight, similar to the weight of a few goose feathers.
From performance point of view, the TEG has substantiallyhigher power density than the traditional generator in terms ofboth power-to-volume ratio and power-to-weight ratio due to
Out
put v
olta
ge (
V)
Time (s)
Water turbine
TEG
TEG
Air flow
Water flow
Water pipe
Stator
Rotator
Inertiamass
Swinginghand
Wind turbine
0 3 6 9 12 15
0
1
2
3
4
5
6
WindWaterBody motion
Figure 7 | Demonstrations of the triboelectric generator for harvesting ambient energy. (a) Harvesting energy from light wind at a flow speed of
6 m s� 1 by the triboelectric generator for powering an array of spot lights (scale bar, 3 cm). Inset: a wind turbine that transmits torque to the
triboelectric generator (scale bar, 5 cm). (b) Harvesting energy from water flow at a flow rate of 5.5 L min� 1 by the triboelectric generator for
powering an array of spot lights (scale bar, 5 cm). Insets: tap water is directed into a water turbine through a water pipe (top; scale bar, 2 cm);
upward view of the water turbine (bottom; scale bar, 7 cm). (c) Harvesting energy from body motion by the triboelectric generator that is being
gently swung with a hand for powering an array of spot lights (scale bar, 5 cm). Inset: the hand-held triboelectric generator with two pieces of inertia
mass attached to the rotator (scale bar, 5 cm). (d) Output voltage of the power-supplying system when the triboelectric generator is driven by the
much smaller volume and weight. The high power densityimparts two major advantages to practical applications of theTEG. First, it is superior to the conventional generator as a small-sized power source for self-powered electronics, for example,harvesting human motions for powering or charging portable/wearable gadgets. In these applications, size and weight manage-ment become critical issues. Second, the significant power densitymakes the TEG potentially advantageous in large-scale powergeneration for stationary power plants, although the feasibilityneeds to be solidly validated with further investigations.
From cost point of view, the TEG on the basis of surfacecharging effect only needs very small amount of materials. Theyare conventional thin-film insulating materials and metals ofvarious kinds that are abundantly available. Besides, it has asimple structure and straightforward fabrication process. As aconsequence, the TEG is extremely cost-effective, which is anunparalleled advantage compared with any other power genera-tion techniques. The significantly low cost of the TEG is a keyadvantage for its potential widespread applications.
Last but not the least, our unique 2-dimensional-planargenerator owns distinctive applicability in a variety of circum-stances. The usual generator has difficulty being made into aplanar structure due to reasons such as poor properties of planarmagnets, limited number of turns achievable with planar coilsand restricted amplitude of displacement36. In comparison, theTEG offers a straightforward and even sole solution to addressingrotation sliding between two surfaces. For example, it can bepossibly integrated into a brake system in automotive and otherapplications where a brake rotor and brake pads have relativecontact rotation. Moreover, due to the simple rotator–statorstructure, our generator provides a much easier and moreconvenient way to address common rotating motions. Forexample, with very little modification, the TEG can takeadvantage of rotating shafts that are commonly found intransmission systems, as clearly demonstrated in Fig. 7 andcorresponding Supplementary Movies 10–12. Besides, enabled bybroad choices of materials, the TEG with particular properties canmeet special needs. For instance, it can be fabricated from organicbiocompatible materials for healthcare and other bio-relatedapplications. Finally, it is the unique solution when installationspace is constrained. Therefore, our generator enables uniqueapplications in many circumstances where the usual generatorcannot be implemented, although both of them utilize rotationfor power generation.
In summary, we developed a new type of planar-structuredelectricity-generation method (TEG) to convert mechanicalenergy using triboelectrification effect, a universal phenomenonupon contact between two materials. On the basis of the stator–rotator structure that has arrays of micro-sized radial sectors, theTEG produced significantly high output power for sufficientlypowering as well as charging conventional consumer electronics.It could effectively harvest a variety of ambient energy frommotions such as air flow, water flow and even body motion.Furthermore, the combination of the TEG and a power manage-ment circuit demonstrated the immediate practicability of usingthe TEG for everyday power needs. Given its exceptional powerdensity, extremely low cost and unique applicability, the TEGpresented in this work is a practical approach in convertingmechanical motions for self-powered electronics as well aspossibly for producing electricity at a large scale.
MethodsFabrication of a TEG on hard substrates. Stator: (1) Cut a square-shaped acrylicsheet as a substrate with a dimension of 13 cm by 13 cm by 3 mm using a lasercutter; (2) Drill through-holes on edges of the substrate for mounting it on a flatstage by screws; (3) Create trenches on top of the substrate using laser cutting.
These trenches define the patterns of the two sets of complementary radial-arrayedelectrodes; (4) Deposit a layer of Ti (10 nm) and then a layer of Au (100 nm) on thesubstrate in sequence using an electron-beam evaporator; (5) Connect two leadwires respectively to the electrodes; (6) Adhere a thin layer of FEP (25 mm) onto theelectrode layer. Rotator: (1) Cut a disc-shaped acrylic substrate with through-patterns that consist of radial-arrayed sectors using a laser cutter. The rotator has adiameter of 10 cm and a thickness of 1.5 mm; (2) Drill a through-hole that hasa D-profile at the centre of the rotator; (3) Use Ar/O2 plasma (100 W) to do surfacetreatment on the substrate for 1 min; (4) Deposit a layer of Ti (10 nm) and then alayer of Cu (200 nm) on the rotator in sequence using a DC sputterer.
Experimental setup for electric measurement. (1) Mount a rotary motor in aninverted way on a three-dimensional linear positioner; (2) Insert the D-profile shaftof the motor into the central hole of the rotator; (3) Align the rotator and the statorto make them in coaxial alignment by using the linear positioner; (4) Adjust heightof the linear positioner so that the rotator and the stator are in contact.
Fabrication of a TEG on flexible substrates. Stator(1) Cut a disc-shapedpolyimide substrate (25 mm) as a substrate using a laser cutter; (2) Use photo-lithography (negative photoresist) to create exposed windows that define electrodeson the substrate; (3) Deposit metal layer by e-beam evaporation, followed by lift-offprocess to generate the electrode pattern on the substrate; (4) Connect two leadwires respectively to the electrodes; (5) Adhere a thin layer of FEP (25 mm) on topof the electrode as an electrification layer. Rotator: (1) Cut a disc-shaped polyimidesubstrate (25mm) as a substrate with through-patterns that consist of radial-arrayed sectors using a laser cutter; (2) Drill a through-hole that has a D-profile atthe centre of the rotator; (3) Use Ar/O2 plasma (100 W) to do surface treatment onthe substrate for 1 min; (4) Deposit a layer of Ti (10 nm) and then a layer of Cu(200 nm) on the rotator in sequence using a DC sputterer.
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AcknowledgementsThe research was supported by the U.S. Department of Energy, Office of Basic EnergySciences (Award DE-FG02-07ER46394), NSF (0946418) and the Knowledge InnovationProgram of the Chinese Academy of Science (Grant No. KJCX2-YW-M13). Patents havebeen filed on the basis of the research results presented in this manuscript. We also thankYannan Xie for his help in setting up the water turbine.
Author contributionsG.Z., J.C. and Z.L.W. designed the TEG. G.Z. and J.C. fabricated the TEG and did electricmeasurement. G.Z., J.C. and Z.L.W. analysed the experimental data, drew the figures andprepared the manuscript. T.Z. designed and built the power-supplying system. Q.J. didfinite element simulation via COMSOL.
Additional informationSupplementary Information accompanies this paper at http://www.nature.com/naturecommunications
Competing financial interests: The authors declare no competing financial interests.
Reprints and permission information is available online at http://npg.nature.com/reprintsandpermissions/
How to cite this article: Zhu, G. et al. Radial-arrayed rotary electrification for highperformance triboelectric generator. Nat. Commun. 5:3426 doi: 10.1038/ncomms4426(2014).
